Nokia 6680 RM-36 Service Manual page 293

Appendix A: RF Troubleshooting
span setting. The output level of the VCO should be about -25 dBm during GSM TX burst.
3.1.3.2.1.1 Replace TX VCO G7502
3.1.3.2.2 Replace balun T7503
3.1.3.3 VCTCXO frequency and output level ok?
• Measurement can be done with an oscilloscope and a probe.
• Connect the probe to C7529 (or C7582)
The frequency of the VCTCXO should be quite exactly 38.4 MHz and level about 0.5 - 0.9 Vpp.
•
Example of the correct VCTCXO output signal is presented in figure
1.24 V)".
3.1.3.3.1 VXO-voltage ok? (=Vdig).
• Measurement can be done with an oscilloscope and a probe
Connect the probe to C7560 (or C7526, C7513)
•
• VXO-voltage should be about 2.5 V
3.1.3.3.1.1 C7560, C7513, C7526 and C2214 ok?
• Check that components are in place and solder joints are ok
• Disconnect the power supply from the phone and use an ohmmeter to find out if the VXO-line is
short-circuited to the ground. If short-circuit is found replace C7560, C7513, C7526 and C2214. If
replacing does not help then go to the next steps.
3.1.3.3.1.2 Replace Retu
3.1.3.3.1.3 Replace Hinku (N7500) or Vinku (N7501) or VCTCXO (G7501) or all three components
3.1.3.3.2 BB AFC-voltage ok?
• Measurement can be done with an oscilloscope and a probe
• Connect the probe to R7509 (or C7533)
• AFC-voltage may vary between 0.1 - 2.3 V. Typical value is 1.2 V. Phoenix "RF Controls" tool can be
used to change the AFC value. Voltage level should be about 0.1 V with AFC value -1024 and about
2.3 V with AFC value 1023.
3.1.3.3.2.1 Low pass filter components R7509 and C7533 ok?
• Check that components are in place and solder joints are ok
• Disconnect the power supply from the phone and check R7509 resistance value with an
ohmmeter.
• Use an ohmmeter to find out also if the AFC-line is short-circuited to the ground. If short-circuit is
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6.5.1 "VCTCXO Output (DC Offset
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